Campylobacter infection, generally food-borne, is a significant global public health problem, representing the leading cause of enteretis in humans. As with most foodborne diseases, the molecular basis for the mechanisms of Campylobacter infection is poorly understood. As the total genomic sequence of C. jejuni subsp. jejuni has recently become available, the next major step is to investigate the function of the genes/proteins revealed by the genome project and how they are expressed during in vivo culture conditions. Inspection of Campylobacter gene expression with a mammalian host should provide us with clues to he mechanisms utilized by Campylobacter to cause disease. During infection of the host, microbial pathogens must survive and replicate in diverse conditions and environments, the infectious process is typically governed by virulence and colonization factors. The availability of iron in the host is a key environmental signal for human pathogens such as Campylobacter which appears to allow them to sense that they have invaded a mammalian host. As a first step in the identification of genes encoding colonization and virulence factors we propose to address Campylobacter gene/protein expression response to iron availability in different environments. More specifically, C. jejuni gene/protein expression in iron-deplete and iron- rich media will be compared. It is anticipated that not only will proteins involved in iron metabolism by identified, but other iron regulated proteins, such as virulence factors, also will be identified using the strategies outlined in this proposal. As a second sep, iron-regulated genes differentially expressed in several biological niches during the stages of colonization and infection also will be addressed using three different models: (i) tissue culture monolayers of human INT407 embryonic intestinal cells; (ii) the in vivo rabbit ileal loop system; and (iii) the rabbit in vivo tissue chamber implant model. Identification of genes commonly or differentially expressed during infection in these in vivo model systems should lead us to a better understanding of Campylobacter pathophysiology.